1. Field of the Invention
The present invention relates to an address generator and, more particularly, to a zigzag scanning address generator for scanning in a zigzag pattern.
Korean Patent Application No. 93-09910 is incorporated herein by reference for all purposes.
2. Description of Related Art
A zigzag address scanning method can be adapted to video encoders for use in a video phone or video conferencing apparatus and to any ordinary video device for realizing a high quality picture. In particular, the method can be adapted to a video compressing method for high definition television (HDTV) systems using next-generation digital compression techniques.
During data transmission, video data compression is performed by, e.g., a discrete cosine transform (DCT) operation, by quantization or by variable-length coding. Among these methods, the DCT method produces coefficients which are generally concentrated in a low-frequency area after the DCT and attendant quantization operations are performed. Therefore, if the coefficients are sequentially arranged from a low-frequency area to a high frequency area, an irregular arrangement results, e.g., with the larger coefficient values occurring in the low-frequency area while the smaller coefficient values (close to zero) being concentrated in the high-frequency area.
In the DCT method, quantization coefficients which are sequentially arranged can be further categorized by scanning pattern, i.e., into an orthogonal scanning method and a zigzag scanning method. Although the DCT coefficients are concentrated in the low-frequency area, as described above, the orthogonal scanning method whereby sequential scanning is performed from the low-frequency area to the high-frequency area, performs data compression inefficiently. On the other hand, the zigzag scanning method, whereby scanning is performed in a zigzag pattern starting from the low-frequency area, in which large coefficient values are concentrated, permits transmission of large coefficient values intact but omits the zeroes occurring in high-frequency areas (where zeroes are frequently encountered) and transmits only the number of successive zeroes, thereby performing more effective data compression.
In FIG. 1, a 2.sup.n .times.2.sup.n block of on-screen video data is scanned in a specified order, i.e., in the order following the arrow marked with a dotted line. In other words, when the data is recorded to or read from the memory wherein 2.sup.n .times.2.sup.n on-screen video data is stored, the data is scanned in a zigzag order. When data is read from or recorded to the memory, the sequentially increasing address counter used in a conventional memory address-generator cannot be used to perform zigzag scanning.
For reasons of compression efficiency, the zigzag scanning method has been designated as one internationally standardized technique for digital video compression, e.g., adopted by the Joint Photographic Experts Group (JPEG) with respect to still video signal coding and, for telecommunication system video compression, specified as international standard method H.261. However, in spite of its inherent advantages, the zigzag scanning method is still not generally used due to inconveniences in its implementation.